Al.sub.x ga.sub.1- N is a compound semiconductor that is ideally suited for devices in the visible and the ultraviolet parts of the spectrum. Its band gap is tunable from 365 nanometers (at x=0) to 200 nanometers (at x=1) and is direct over the entire alloy composition. This makes the material ideally suited for intrinsic ultraviolet sensors with responsivities sharply peaked at a wavelength corresponding to the band edge. Such sensors have potential commercial applications in the areas of flame safeguard and fire control.
Ultraviolet detectors and, specifically, detectors of gallium nitride are well known in the art. For example, Khan et al, U.S. Pat. Nos. 4,614,961 and 4,616,248, disclose gallium nitride devices. One device is an ultraviolet detector comprising a sapphire base, an aluminum nitride matrix matching layer, and an aluminum gallium nitride active layer. However, made by conventional metal organic chemical vapor deposition (MOCVD), the disclosed device has a peak sensor responsivity at 365 nanometers. The device generally does not provide a broad response across the expanse of the ultraviolet range.
Others have deposited gallium nitride layers over basal plane sapphire substrates using metal organic chemical vapor deposition; see Khan et al, Applied Physics Letters, 58, 526 (1991); Amano et al, Japanese Journal of Applied Physics, 29, L205 (1990); and Nakamura et al, Applied Physics Letters, 58, 2021 (1991).
The deposition of various aluminum gallium nitride layers in various temperature environments has also been well documented, see Khan et al, Applied Physics Letters, 58, 1515 (1991); Khan et al Applied Physics Letters, 58, 2408 (1991); Khan et al, Applied Physics Letters, 60 (11), 1366 (1992); and Khan et al, Applied Physics Letters, 56, 1257 (1990).
However, no prior art gallium nitride ultraviolet device has provided a detector having the level or range of responsivity necessary to provide sensitivity over the broad ultraviolet range while still avoiding interferences created by visible and infrared wavelengths.